The present invention relates to a constant speed regulator for a DC motor the regulator being capable of substantially eliminating the ripple component in the DC component which varies in response to the rotational speed of a DC motor, thereby ensuring stable speed control of the DC motor.
In a prior art constant speed regulator for a DC motor, a transistor is turned on and off in response to output of a generator mechanically coupled to a DC motor, and the output of the transistor is applied to a differentiating circuit to form the trigger pulse to trigger a monostable multivibrator. The monostable multivibrator produces a square waveform output whose duty cycle varies in response to the frequency of the trigger pulses, and the output of the monostable multivibrator is integrated by an integrator to derive a DC voltage which varies in response to the rotational speed of the DC motor. In response to the DC output voltage, a control transistor is so operated that when the rotational speed of the DC motor increases, the control transistor provides a signal that decreases the rotational speed, while when the rotational speed decreases, the control transistor provides a signal that increases the rotational speed.
The DC output voltage of the speed regulator contains the ripple component whose frequency is dependent upon the output frequency of the generator mechanically coupled to the DC motor. When the frequency of the ripple component is so high that the ripple component may be absorbed by the inertia of the rotor of the DC motor, the ripple component will not adversely affect the operation of the DC motor. However, when the output frequency of the generator is very low, the ripple component tends to cause vibrations of the rotor of the DC motor.